Chris Gasper was talking about this a couple of weeks ago. his scenario was this:
Pats send Mac and their second for LV's 1st (pick 7).
His reasoning was that Josh really liked Mac, as did Ziegler. He was THEIR pick, according to Gasper. If they don't see a better QB at 7 - he didn't think they would - they get their QB.
For the Pats, he said BB wasn't thrilled with Mac right now (we can all see that) and that Kraft really loved Jimmy G and BB liked him, as well. And to top it off, Jimmy was a fan favorite here, undeniably.
So in Gasper's scenario, the Pats sign Jimmy G and have picks 7 and 14 to play with and bring in some talent, while the Raiders get their QB for their first pick (two years and lots of playing time under his belt and still with 3 years of cheap control) AND get a mid-round second to boot.
I hate to say it, but it makes sense when you look at it that way. If BB and RK prefer Jimmy and can get him, this wouldn't surprise me at all.